Top Democratic lawmakers are rushing to extend the cap on police and firefighter pay raises that some say has helped keep property tax bills in check. But local officials say the bill expected to be voted on today in both the Assembly and state Senate includes too many loopholes to be effective.

Since 2011, raises for local police and firefighters have been limited to 2 percent if contract disputes were settled, as many are, through the state’s binding arbitration process. Statewide, the average property tax bill rose to a record $7,988 in 2013, but that rate of growth has slowed while this cap and another that limits overall increases in the local tax have been in place.

The salary cap expires on Tuesday, a deadline written into the original law as a compromise between the Democrats who control the Legislature and Governor Christie, a Republican.

Before the cap was in place, unions were often given raises of around 4.5 percent. That figure is now 1.9 percent after the cap, according to a recent report issued by a task force set up to study the cap’s effectiveness.

Without a full extension of the current cap, the local officials warn, cuts in services are likely.

“Unless you can find additional dollars or a leprechaun pot of gold, you have to cut services,” said Bill Dressel, executive director of the New Jersey State League of Municipalities.

But the unions that represent police officers and firefighters working for New Jersey municipalities and counties say the cap has been too restrictive and has taken too much bargaining power away from their members, who by law aren’t allowed to go on strike.

“The bill contains critical provisions that ensure that a collective bargaining unit can only be exposed to the arbitration-cap law once,” the New Jersey State Policeman’s Benevolent Association said in a statement.

The Democrats’ bill would extend the 2 percent cap until Dec. 31, 2017. But it carries a key provision in the original bill that permitted governments to cap raises only once. The original bill, however, covered a period of just over three years, roughly the duration of most of the union contracts.

The new bill would permit arbitrators to award raises of up to 3 percent annually if the unions agree to pay more for benefits or to cuts in the number of jobs.

The measure would also change the process through which arbitrators are selected, and it would give the arbitrators themselves a pay raise.

The cap was a big part of Christie’s so-called tool kit to combat property tax bills — along with the broader 2 percent cap on local property tax hikes, both passed with bipartisan support in 2010 — and though property taxes have continued to rise, the caps have helped restrain growth three straight years.

Democratic legislative leaders say their bill strikes the right balance between the concerns of taxpayers and the unions, including some that supported Democratic lawmakers and Christie’s challenger in last year’s elections.

Republicans, meanwhile, have their own bill to extend the cap permanently. Assemblyman Declan O’Scanlon, R-Monmouth, said the cap on arbitration awards can’t be lifted while the broader limit on property tax increases is still in place.

“These are not intellectually consistent positions,” said O’Scanlon, sponsor of the Republicans’ bill.

O’Scanlon also stressed the need to lift the limit on governments’ use of the 2 percent cap to just one contract negotiation.

Sweeney and Prieto were both not available for comment on the issue Wednesday.

He added, “I think that there is fundamental disagreement with Assemblyman O’Scanlon’s analysis.”

Many expect it will take behind-the-scenes negotiations to settle the differences.

A spokesman for the governor said on Wednesday that the Democrats’ bill is still under review.

“What the governor has been 100 percent clear about is that the 2010 reform, which was overwhelmingly bipartisan, has been objectively proven to be effective in providing relief to local governments and property taxpayers,” the spokesman, Kevin Roberts, said. “Local elected officials from every part of the state agree and have called for its renewal for exactly that reason.”

Both the New Jersey State League of Municipalities and the New Jersey Association of Counties have opposed the current draft of the Democrats’ bill. The problem, both organizations say, is that the cap is not permanent and doesn’t ensure that governments that have taken advantage of the cap can do so again.

“This provision dilutes the impact of the cap,” Dressel said. “It basically amends the current law so, effectively, all communities that were subject to the 2 percent cap in negotiations and arbitration previously would not be able to take advantage of it moving into the future.”

But the Policemen’s Benevolent Association said the key to the bill is not making the cap permanent.